Fracturable adhesive backing

ABSTRACT

A process and apparatus for selectively compressing paper stock of the type which is used as a protective backing sheet for adhesive-coated systems. The process comprises use of a novel compression tool, the precise characteristics of which depend on the paper stock being utilized. The compression tool comprises a blunt, rotatable, circular, working edge which has a radius of at least 0.02, but preferably at least 0.04 inches in diameter and at least one half of the thickness of the paper being weakened. This tool advantageously comprises the compressing edge, being mounted integrally with a bearing surface which makes pressure control easier and limits penetration of the tool. In the preferred embodiments of the invention, the bearing surface is faced with elastomeric material. Disclosure is also made of a novel release sheet and adhesive sheet assembly which is manufactured utilizing the process and apparatus of the invention.

United States Patent [191 Keck et a1.

1 March 6, 1973 FRACTURABLE ADHESIVE BACKING [75] Inventors: Jerry L.Keck, Chicago; James Robert Rowley, Calumet Park, both [22] Filed: Aug.6, 1971 [21] Appl. No.: 169,653

[56] References Cited UNITED STATES PATENTS 3,558,425 l/1971 Massari..161/406 X 3,570,337 3/1971 Morgan ..83/12 3,035,957 3/1962 Morgan..161/411 X 3,006,793 10/1961 wheeler ..161/411 X Brown ..161/117 Starr..161/117 Primary Examiner-Daniel J. Fritsch AttorneyCesari & McKenna [57 ABSTRACT A process and apparatus for selectively compressing paperstock of the type which is used as a protective backing sheet foradhesive-coated systems. The process comprises use of a novelcompression tool, the precise characteristics of which depend on thepaper stock being utilized. The compression tool comprises a blunt,rotatable, circular, working edge which has a radius of at least 0.02,but preferably at least 0.04 inches in diameter and at least one half ofthe thickness of the paper being weakened. This tool advantageouslycomprises the compressing edge, being mounted integrally with a bearingsurface which makes pressure control easier and limits penetration ofthe tool. In the preferred embodiments of the invention, the bearingsurface is faced with elastomeric material. Disclosure is also made of anovel release sheet and adhesive sheet assembly which is manufacturedutilizing the process and apparatus of the invention.

3 Claims, 7 Drawing Figures FRACTURABLE ADHESIVE BACKING BACKGROUND OFTHE INVENTION There have always been a number of problems associatedwith the use of adhesive-backed papers such as those used as labels,etc. These problems, largely related to avoiding premature contact ofthe adhesive with other objects, have been largely overcome by the useof releasable backing sheets. The need for convenient removal of labelsor other adhesive papers from these release-coated backing sheets raisednew problems and a considerable amount of inventive effort has beenundertaken in solving such problems.

For example, U.S. Pat. No. 3,035,957 to Morgan disclosed a chemicalembrittlement process which is used to provide embrittled lines along abacking sheet and thereby facilitate the breaking of the backing sheetand the mechanical removal of the sheet from the adhesive. Such aprocess avoids the need to mechanically score and cut through therelease-coated sheet. The avoidance of cut-through eliminates theproblem associated with the seepage of adhesive through the cuts. On theother hand, use of chemical compositions present handling problems inthe plant, leave an unsightly marking on the sheet, and have a tendencyto result in a product that will flake and lint in use.

U.S. Pat. No. 2,319,272 to Starr includes a disclosure of other methodssuch as knife-scoring, scorching and abrasion of a sheet, to selectivelyweaken linear portions therealong, on an adhesive-coated rubber patch.Starrs rubber patch may provide an especially high degree of cushioningfor the backing sheet being processed; the Starr patent does teach theutility of such support, however.

Thus it is seen that the prior art has utilized various linear weakeningtechniques such as applying thin lines of acid to chemically weakenselected linear portions of the backing sheet, abrading the sheet toselectively weaken it along the abraded line, cutting through part ofthe sheet along predetermined lines, etc.

One problem which has interfered with obtaining the maximum projectadvantage from these processes has been the requirement to leave arather high safety margin to avoid cutting a slit through the paperduring each process. Such cut-through, of course, tends to allowadhesive to seep through the backing sheet and stick to adjacent sheets,thereby completely obviating the advantage sought by using anon-perforating process to selectively weaken the paper.

While it is undesirable to have such adhesivepenetrable weak-spots inthe backing sheet, it is equally undesirable to have tear lines whichare supposed to crack open when deliberately flexed by the user butwhich do not do so because the line is not weak enough. Therefore, itwill be understood that a selectively weakened line must be deep enoughto allow easy splitting but also must be strong enough so that it willnot split when it is not supposed to split (for example, by tearing atsplit points not subjected to deliberate flexing. Such secondary splitlines are often provided on release sheets of the co-calleduniversal-split type and which are particularly described in U.S. Pat.No. 3,006,793 to Wheeler.)

In many prior art backing sheets, the extra lines were so weak that thesheet would tear at the extra lines and greatly slow down the strippingof the backing sheet and consequently, delay the label-applying process.The compressed paper lines of the instant invention have a relativelyhigh residual strength when compared to the low resistance to breakagewhen flexed along a score line. As has been indicated above, thisstrength is a consequence of the uniformity with which weakening may beachieved by use of the present method and apparatus.

SUMMARY OF THE INVENTION Therefore, it is an object of the presentinvention to provide an improved process for controllably weakening aprotective, release-coated backing sheet for use in backing of anadhesive-coated label stock or the like.

Another object of the invention is to provide improved apparatus forselectively weakening paper along linear portions thereof.

Another object of the invention is to provide a superior process formaking a release-sheet-backed label display assembly.

A further object of the invention is to provide an improved apparatusfor selectively weakening linear section of paper sheet.

Another object of the invention is to provide such apparatus whichperforms well when applied to resincoated paper surfaces.

Other objects of the invention will be obvious to those skilled in theart on reading the instant application.

The above objects have been substantially achieved by a processutilizing a novel tool having a working edge of a relatively largeradius with respect to the paper to be compressed, and simultaneouslyweakened by use of the tool. The use of such an edge has been found toallow a compressing depth of up to percent or more of the paperthickness without danger of excessively weakening, or cutting through,the paper being processed. The compression of paper caused by use ofthis tool results in a weakened path which parts easily along a sheetwhen one bends the sheet along the line of the compressed path. However,the processed sheet also provides a suitable shield against seepage ofadhesive. The invention when used with relatively heavy paper, such asclay-coated kraft tag stock of 78 lbs. per ream, does not have anysignificant tendency to part at embrittled and compressed linear pathsalong which splitting is required during removal of the backing from anadhesive sheet. This is a consequence of the relative uniformity withwhich the linear paths can be formed: enough compression can be achievedto give an easysnapping line but the residual tensile strength is greatenough to prevent accidental tearing.

The radius of the edge of the embrittling tool of the invention is fromabout 0.020 inches to 0.100 inches depending on the thickness of thepaper. It has been determined that there should be a bearing surfacemounted with compression edge to assure maximum ease of control over theline of compression when light paper stock is being processed. In suchcases the cutting edge protrudes a distance from the bearing surface ofabout percent of the papers thickness. By light paper stock is meantpaper of about 80 lbs per ream or heavier and particularly paper of lbsor more per ream. With heavier paper bearing surfaces are not needed tomoderate compression, but they are helpful for carrying traction ringsand for moderating the rate of compression.

ILLUSTRATIVE EMBODIMENT OF THE INVENTION In this application andaccompanying drawings are shown and described a preferred embodiment ofthe invention. Various alternatives and modifications thereof, aresuggested, but it is to be understood that these are not intended to beexhaustive and that other changes and modifications can be made withinthe scope of the invention. The suggestions herein are selected andincluded for purposes of illustration in order that others skilled inthe art will more fully understand the invention and the principlesthereof, and will be able to modify it and embody it in a variety offorms, each as may be best suited in the condition of a particular case.

In the drawings:

FIG. 1 is a plan view of a segment of a typical backing sheet of theuniversal-split type mounte over an adhesive-coated sheet.

FIG. 2 shows a cross-sectioned, somewhat schematic view of the backedadhesive sheet of FIG. 1.

FIG. 3 is a side view of one compression wheel constructed according tothe invention.

FIG. 4 is an elevation taken normal to the axial direction of thecompression wheel of FIG. 3.

FIG. 5 is an elevation of another compression wheel constructedaccording to the invention and taken normal to the axial directionthereof.

FIGS. 6 and 7 show a particularly advantageous tool formed according tothe process of the invention.

Referring to FIGS. 1 and 2, it is seen that an adhesive-sheet assembly10 comprises an adhesive-bearing sheet 12, a coating of adhesive 14firmly attached thereto, and an adhesive-backing sheet 16. Hacking sheet16 is only moderately adherent to adhesive 14 and may be convenientlypeeled therefrom. Such peeling is facilitated by bending sheet assembly10 toward the label-bearing side and thereby causing it to crack along aline 18 as shown in FIG. 2. The bending causes cracking along thecompressed paper 20 of lines 18. This bending will cause an edge of thesheet 16 to become exposed and readily grippable for pulling theremaining part of 16 from the assembly 10.

As indicated in FIG. 1, a backing sheet normally contains a number ofweakened lines 18 so that there will be at least one present on thesmallest item likely to be cut from the sheet by a manufacture. Inpractice, this means that most users will be peeling backing sheet 16from items containing a plurality of lines 18, some of which are notintended to be ruptured by that particular user. Their remaining intactallows a quick removal of the backing sheet by the user.

FIGS. 3 and 4 illustrate a compression wheel particularly useful inembrittling a relatively light backing sheet. This wheel is mounted onan axis 32 and comprises, in addition to a semi-circular compressingedge 34 having a radius R1 of 0.04 inches, a pair of integrally mountedshoulders 36 which provide means to limit the degree of compressionalong linear portions of a backing-sheet being treated.

FIG. 5 illustrates a compression wheel which has a radius R of 0.05inches. Wheels of such radii do not absolutely require limitingshoulders when used to selectively embrittle backing sheets of 8 mils ormore in thickness, although use of such shoulders to moderatecompression or to hold traction rings is most often desirable.

It is desirable to operate with 78 lb per ream paper. It is lesstroublesome to make universal-split type assemblies with such paper thanwith paper of a smaller weight basis. Such 78-lb paper is about 0.004inches in thickness when clay-coated to provide a suitable surface forreceiving a release coating, e.g. a silicone coating. With such paper, aradius of about 0.025 inches on the compressing edge of the tool isabout optimum.

The process can be run most smoothly, however, when coated tag papers of7 to 8 mil caliper are used with a scoring wheel of 0.05 mils in radiusand it is such a paper that is most advantageous for use in the processof the invention. When such papers are properly compacted, they beakwith a sharp snap on being bent about 60 to toward the side which wascontacted by the scoring wheel. The compressing is advantageously doneby applying the scoring tool to the release-coated side of the paper.This tends to be less stressful on the release coating; strain appliedfrom the opposite side from the release coating often ruptures otherwisesuitable release coatings. The pressure is such that the paper isweakened to have a tensile strength of between about 5.0 and about 18lbs per when tested on an Instron-type tensile-testing instrument ModelNo. TM 481, an instrument commonly known to the art and sold by InstronCorporation. Most advantageously, the strength of compression lineranges between about 6 to l2 pounds. And this is less than about 8 to 15percent of the tensile strength of the paper before it is embrittled bycompression.

The test procedure is as follows:

Sample Size: l-inch wide; 1 inch between clamp-jaws Crosshead Speed: 1inch per minute Chart Speed: 10 inches per minute In general, papershould be weakened to less than about 20 percent of its originalstrength by the process of invention.

FIGS. 6 and 7 show a particularly advantageous embodiment of theinvention. In this embodiment of the invention, a compression wheelassembly 40 comprises set into a groove 45 on each side of wheel 30, aresilient wheel such as an O-ring 42. The wheels 42 help to assure arelatively uniform compression rate and are of particular value inmaintaining traction of the wheel on the paper and this assuring itscontinuous rotation. As seen in FIG. 8, they are compressed when engagedwith paper sheet 44 against a firm backing support member 50. Normallythese wheels are formed of an elastomeric material such as a siliconerubber elastomer, or N type of synthetic rubber. An O-ring about 0.103in thickness is appropriate; an I-l2-l49 O-ring is particularlysuitable, and may be spaced conveniently about 0.15 inch or so from thecompressing wheel itself.

The total width 46 of assembly 40 is about 0.75 inches. Wheels 42 and 30extend about 0.125 inches outwardly from the main body 48 of the wheel.

Production speeds of well over 200 feet per minute are easily attainedusing the scoring process of the invention because it does not involve amechanical engagement with the paper as is required in conventionalscoring or abrading processes, and it does not require controlledapplication of a chemical reagent as is required by use of chemicaletchants. Indeed the process is not at all limiting of line speed inmost cases, that being more limited by drying times. However, when theprocess is applied to weakening paper in operations not limited by suchfactors as drying time, it allows excellent improvements in line speedswhile maintaining a relatively more uniform weakening of the paper alongthe line of compression.

It has been discovered that the most satisfactory procedure to use is tocompress the paper being treated by application of compression from therelease side. This has the special advantage of eliminating disruptionsin the release coating which were noticed to occur with some frequencywhen the coating was extended by strain caused by the scoring toolapplied to the noncoated surface of the release paper. Such disruptions,of course, result in an undesirable sticking of adhesive coating labelsto the paper substrate and interfere with the convenience with which themounted labels can be used.

It has also been found that the rupture of the release paper is moreuniformly controllable when the paper is bent toward the grooved siderather than away from it.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which mightbe said to fall therebetween.

What is claimed is:

1. In an adhesive-sheet assembly of the type consisting essentially of(a) an adhesive-bearing sheet material and (b) a protective, peelable,backing sheet having a surface coated with a release agent, said surfacein contact with said adhesive, the improvement wherein said backingsheet comprises at least one linear compression-embrittled paththerealong of relatively low resistance to bending stress and whereinsaid path is of embrittled paper compressed to less than 50% of itsoriginal thickness and less than 20% of its original tensile strengthalong said linear path, and wherein the non-compressed portion of thebacking sheet is at least 0.004 inches thick and wherein said compressedpath is indented into that side of said sheet coated with said releasecoating.

2. A release-sheet backed adhesive-sheet assembly of the type defined inclaim 1 wherein said release coating is a silicone-based coating.

3. A release-sheet-backed adhesive-sheet assembly of the type defined inclaim 1 wherein said release sheet is formed of paper about 0.007 inchesthick and wherein said linear path has a tensile strength of from 5 to18 psi.

1. In an adhesive-sheet assembly of the type consisting essentially of(a) an adhesive-bearing sheet material and (b) a protective, peelable,backing sheet having a surface coated with a release agent, said surfacein contact with said adhesive, the improvement wherein said backingsheet comprises at least one linear compression-embrittled paththerealong of relatively low resistance to bending stress and whereinsaid path is of embrittled paper compressed to less than 50% of itsoriginal thickness and less than 20% of its original tensile strengthalong said linear path, and wherein the non-compressed portion of thebacking sheet is at least 0.004 inches thick and wherein said compressedpath is indented into that side of said sheet coated with said releasecoating.
 2. A release-sheet backed adhesive-sheet assembly of the typedefined in claim 1 wherein said release coating is a silicone-basedcoating.